In general, a conventional nail clipper is provided with upper and lower blades constituting a blade body, which are in the form of inclined surfaces with symmetric structures. The upper and lower inclined surfaces are formed in slightly concave surfaces having the same curvatures. The upper and lower blades having the constructions as such can be manufactured by simultaneously grinding the ends of the blade bodies using grinding media which have a radius corresponding to the curvature of the ends of the blade bodies being horizontally engaged with each other.
FIGS. 1 to 5 are schematic views each illustrating the classification of the engagement pattern of the upper and lower blades for various nail clippers. FIG. 1 shows constructions of a conventional nail clipper, wherein the blades of the upper and lower blade bodies are engaged with each other with a curve (A-B-C) in the X-Y plane. In the drawings, points A and C indicate the opposite ends of a blade, respectively and the point B is the center of the blade. FIG. 2 shows constructions of another conventional nail clipper, wherein the blades of the upper and lower blade bodies are engaged with each other with a straight line (A-B-C) in the X axis.
Referring to FIG. 1, the upper and lower blades in the prior art are formed in concave curved surfaces when seen from the plan view as shown in FIG. 1(d), so a user's nail can be cut in a circular pattern. However, when seen from the front view as shown in FIG. 1(b), the upper and lower blades are engaged together in a straight line. Therefore, since the user has to cut his/her nail with a circular curved-surface shape using the upper and lower blades to be engaged with in a straight line, some problems are raised therefrom.
In other words, when the user uses a conventional nail clipper having horizontal upper and lower blades as shown in FIG. 1, the end portion of the nail should be inserted between the upper and lower blades to be pressed together. Then, a downward force is applied to the middle convex portion of the nail, while a lifting force is exerted on the opposite edge portions of the nail. At this moment, the forces exerted in the opposite directions, i.e., shearing forces are applied to the nail itself, and the cutting operation of the nail is then performed while the nail is flatly retained between the upper and lower blades. Consequently, whenever the nail clipping operation is performed, stress and strain are repetitiously applied to the nail. Even in a severe case, the conventional nail clipper as described above has drawbacks in that a frail or weak nail may be damaged, or eventually torn or broken.
In order to resolve or lessen the drawbacks in the conventional nail clippers, a variety of technologies have been proposed. For instance, there is a Korean Patent No. 10-0674475 (Jan. 19, 2007) entitled “a method for manufacturing an arc-type blade body, the blade body made therefrom, and a nail clipper having the blade body” which was issued to the same applicant of the present invention. This patent relates to a manufacturing method for a two (2)-dimensional vertical and curve-type blade which is referenced to the present invention, wherein the upper and lower blade bodies are engaged with each other with a vertical curve (A-B-C) in the X-Z plane. The upper and lower blades of the blade body engaged with each other are in the form of an upward curve-shape, when seen from the front view. Since these blades are designed to comply with the cross-sectional shape of the nail having a curved surface, thereby considerably reducing the stress and the strain applied to the nail during the clipping operation. The blade body with the constructions as the above may be a useful technology for the users who want to cut their nails in a straight line following the art of nail fashion like a nail art. However, since the end of the nail is cut in the straight line, it cannot be employed to the case where the user wants to cut the nail in a curve-shape.
In order to solve the problems as described above, as shown in FIGS. 4 and 5, a curve-type blade with a three (3)-dimensional structure may be proposed, wherein the upper and lower blades are engaged with each other in the shape of an upward curve-shape, and at the same time slightly inclined rearward in a direction of the handle, i.e., in a longitudinal direction of the blade body. However, such a proposal is just an idea, which has been regarded as technically impossible up to now to manufacture the curve-type blade having such a geometrical structure.
Meanwhile, a variety of technologies relating to the blade body of the nail clipper have been proposed as following: For example, Korean Patent Laid Open No. 10-2004-0043581 (May 24, 2004), Japanese Utility Model Laid Open Sho49-120419 (Oct. 16, 1974), Japanese Utility Model Laid Open Sho51-119970 (Sep. 12, 1977), Japanese Utility Model Laid Open Sho54-98369 (Jul. 11, 1979), Japanese Utility Model Laid Open Sho54-116468 (Aug. 15, 1979), Japanese Utility Model Laid Open No. 2005-74135 (Mar. 24, 2005), Japanese Utility Model Laid Open Pyoung01-145305 (Oct. 5, 1989), and U.S. Design Pat. No. 371, 636 (Jul. 9, 1996), or the like.
In particular, U.S. Design Pat. No. 371, 636 discloses that the end portions of the upper and lower blades of the nail clipper have inclined curve-type surfaces. However, this patent just discloses such a design for an exterior shape of the nail clipper, but is silent on the technical method how to manufacture such inclined curve-type blades.
Some prior arts in the above list roughly mention about the shape of the nail clipper having an inclined curve-type blade or its usefulness. However, they only raise problems to be solved or suggest idea on the shape of the inclined curve-type blade, but they fail to propose the manufacturing technologies or theoretical backgrounds how to construct and produce the inclined curve-type blade as such.
Generally, the blade grinding work in the manufacturing process of the nail clipper is performed in a short period of time about 1-2 seconds by bringing the blades into contact with the grinding media. At this point, the upper and lower blades should be manufactured to be exactly engaged with each other. However, during a manual or an automatic grinding work, a deviation in the respective grinding depths of the blade is inevitably generated due to the jig of a grinding machine, grinding work conditions, degrees of the worker's skillfulness or the like.
In other words, the grinding work of the blades of the nail clipper may be divided into a manual, a semi-automatic or fully automatic work. Generally, a grinding roller with a radius suitable for the curvature of the curved surface of the end portion of the blade is used in the grinding work. The manual grinding work has a considerable difference in its grinding result depending upon the skillfulness of the worker. Further, in the semi-automatic or fully automatic grinding work there also generates deviations due to the jig or the transporting mechanism or a variety of deviations according to the degree of wear of the grinding media. Because of these deviations, the middle portion of the upper and lower blades is likely to be opened or the gap between the opposite edges of the upper and lower blades are widened after the grinding work, which makes it difficult to obtain a nail clipper having a desired quality.
Meanwhile, a nail clipper of which upper and lower blades are exactly engaged with each other may be manufactured by elaborate manual grinding works. However, in order to mass-produce the nail clipper having a uniform, precise and high quality, a theoretical background and manufacturing technology for production of the nail clipper must be provided to support that. In other words, it is necessary to propose a method for forming an inclined curve-type blade body whose upper and lower blades are exactly engaged with each other regardless of the grinding work condition, so as to mass-produce the blade body with the same quality of which upper and lower blades are precisely engaged with each other without any gap therebetween. At this point, it is very important to provide conditions for the mass production of the blade body having the same quality despite the existence of the considerable deviations in the grinding depth.
However, in the technical fields relating to the nail clipper, there has been yet no technical solution or proposal about how to manufacture the inclined curve-type blade body, whose upper and lower blades are exactly engaged with each other in the 3-dimensional space. Moreover, they are silent on which conditions are required to mass produce the nail clipper having the inclined curve-type blade body with the same quality regardless of the existence of the considerable grinding deviations. This appears to be certain that the technology or method to produce the inclined curve-type blade having such a 3-dimensional structure has not been found up to now. Such assumption as the above can be supported by the fact that there have been no nail clippers having such an inclined curve-type blade among the commercially developed and marketed nail clippers to this date.